Due to the booming development in hand-held or portable electric appliances or utilities, secondary rechargeable batteries or cells are finding ever more extensive applications from day to day. The present invention relates to a charging assembly and a secondary battery set, such as, for example, a nickel/cadmium, a nickel/hydrogen, a nickel/zinc, or a ferrous nickel cell, to be mounted in and matched with the charging assembly, the charging assembly and secondary battery set being furnished with conductive contacts to facilitate transfer of electric power from the charging assembly to the second battery set. The conductive contacts are arranged such that, once force is applied thereto in order to insert the secondary battery set into the charging assembly, a spring will be mechanically compressed to store stress, the spring being arranged to disengage the contacts when a transient temperature rises in response to charging saturation, i.e., after the contacts are brought into conduction to initiate a charging cycle, stress stored in the spring will be released by control of a temperature-responsive saturation testing device and an interface matched thereto. Cutoff of the secondary cell from the charging assembly may be made with respect only to the secondary battery cell, only to the charging assembly, or only to conductive contacts inside the charging assembly, so that charging current in the secondary cell is cut off altogether. The saturation testing device includes a temperature sensor arranged to test the rise in temperature when the cell charging reaches its saturation, and to thereby determine the timing to cut off charging once saturation is reached. Alternatively, a temperature testing means may be provided with conductive contacts in the charging assembly, so that the batter cell is secured in place when inserted into the charging assembly and a stable conduction is made between the entire charging assembly and the cell, so that charging may occur with respect to the cell, the temperature sensor being maintained in a set status until saturation occurs in the cell that is being charged, at which time the cell undergoes a rise in temperature and the temperature sensor responds by driving the charging assembly and the cell into a cutoff status in which the power supply to the secondary cell is cut off and charging current is blocked accordingly.